Abstract  [Aim]  To provide a theoretical basis for the accurate and rapid identification of the instars of Toxoptera aurantia. [Methods]  Seven morphological indices of different instars nymph and adults of both morph from T. aurantia, including body length, body width, head width, antennae length, cornicle length, cauda length and hind tibia length, were measured using a stereo microscope. [Results]  There were differences in each of the seven morphological indices measured among various instars of both apterous and alate T. aurantia. The body length and length of the hind tibia of apterous individuals, and the length of the hind tibia of the alate individuals showed either part, or no, overlap between different instars nymphs and adults, and therefore could distinguish the instars of both morphs of T. aurantia. In addition, the development of the wing base could be regarded as a diagnostic characteristic for differentiating the 3rd and 4th nymph instars of alate individuals. The number of antennal segments could be used as a diagnostic characteristic to differentiate the 1st and 2nd instars from other instars, and cauda shape could be used to differentiate between nymphs and adults. [Conclusion]  Instars of T. aurantia could be accurately and quickly distinguished on the basis of body length and length of the hind tibia, in the case of apterous individuals, and on the basis of the length of the hind tibia, in the case of alate individuals, in combination with auxiliary characteristics such as the development of the wing base on thorax, number of antennal segments of different instars and cauda shape.